This invention pertains to combining space heating and cooling systems with water heating systems. More particularly, the present invention utilizes a heat pump to variously provide space heating or cooling, either alone or in conjunction with water heating, or water heating alone.
The use of heat pumps to provide heat or cool air to an interior space dependent on the refrigerant flow path is well known. The basic elements of such systems include a compressor, an indoor heat exchanger, an outdoor heat exchanger and refrigerant expansion devices. Such a heat pump system is used to heat an interior space by directing refrigerant from the compressor or to be condensed in the indoor heat exchanger, then through an expansion device to the outdoor heat exchanger, where the refrigerant is evaporated and directed to the compressor. The system may be used to cool the indoor space by redirecting the flow of refrigerant in the cycle such that the indoor heat exchanger is the evaporator and the outdoor heat exchanger is the condensor.
Furthermore, it is known that heat pumps may be used to heat water for hot water storage systems.
In order to provide a more economical system, as well as to conserve energy usage, a number of combined systems have been proposed whereby water heating is incorporated in an interior air heat pump space conditioner. Such systems economize on construction by allowing some common elements, such as the compressor and the outdoor heat exchanger, to serve both water heating and space conditioning functions. Such systems economize on energy usage, for example, by utilizing heat removed from the interior space during cooling to heat hot water, rather than discharging all of such heat as waste heat.
U.S. Pat. No. 4,249,390 to Jones disclosed a heat pump waste heating system which utilizes an additional water-refrigerant heat exchanger. This system does not disclose a separate water heating cycle and does not provide for a dedicated refrigerant path to bypass the indoor air heat exchanger.
U.S. Pat. No. 4,311,498 to Miller discloses a desuperheater control system which utilizes superheat to heat water in a refrigeration apparatus. This patent does not provide for heating of air.
U.S. Pat. No. 4,399,664 to Derosier discloses a heat pump water heating system which utilizes two in-line heat exchangers which may be optionally utilized to control the amount of heat recovered by heating water.
U.S. Pat. No. 4,448,037 to Hama et al. discloses a combined cooling, heating and hot water service system. In this patent the heating of hot water is constrained to occur during times of the day when heating and cooling is not required.
U.S. Pat. No. 4,492,092 to Sinoral et al. discloses a combined cooling, heating and hot water system wherein the water heating portion of the system has controls to maintain safe hot water temperatures for domestic use.
U.S. Pat. No. 4,507,938 to Hama et al. discloses a combined heating, cooling and hot water heating system with dual refrigeration devices.
U.S. Pat. No. 4,514,990 to Sulkowski discloses a combined heating, cooling and hot water heating system which requires an extra condensor to remove excess heat from the refrigerant when the system is in the water heating only mode.
A need still exists in the field of combined heat pump-hot water service systems for an economical and practical system. The prior art either requires additional major components, restricts the use of water heating, or does not provide a dedicated path to allow for water heating without operation of the space conditioning. Furthermore, conventional heating and air conditioning expansion valves are not appropriate for use under conditions of water heating alone, and will result in unstable or limited operation.